Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with a radio access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future. Reduction of cost per bit, increase of service availability, flexible use of frequency bands, simple structure and open interface, proper power consumption of a user equipment (UE), and the like are defined as requirements.
A cell selection procedure is a procedure for selecting a cell in which a service is provided to the UE. In general, the UE selects a cell having a highest signal characteristic value by performing a signal measurement procedure with a base station (BS) in all detectable frequency bands. Signal measurement criteria in a universal mobile telecommunications system (UMTS) based on the WCDMA may be found in clause 5.2.5 of the 3GPP TS 25.304 V7.1.0 (2006-12), “Technical Specification Group Radio Access Network; User Equipment (UE) procedures in idle mode and procedures for cell reselection in connected mode (Release 7)”.
Cell selection may be ineffective when using a method of selecting another cell according to criteria on quality or strength of a signal received by the UE from the BS. For example, assume that a first cell and a second cell geographically overlap with each other and operate using different frequency bands, and the UE is located near a boundary region between the two cells. In this case, a signal characteristic value of the first cell and a signal characteristic value of the second cell are almost the same when measured by the UE. However, even in a case where the number of UEs receiving a previous service in the first cell is four and the number of UEs receiving the previous service in the second cell is one, the UE may select the first cell. As a result, a bandwidth that can be simultaneously allocated to the UEs decreases in the first cell. In addition, a small number of UEs provide services in the second cell and thus an idle duration increases. The idle duration is a duration in which an available bandwidth is not used. That is, there is a problem in that the available bandwidth provided in the entire system cannot be sufficiently used.
Accordingly, there is a need for a method of effectively performing cell reselection.